Clearance Hole Size Calculator

The hole the bolt passes through, in all three standard fits, with the drill that makes it.

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Tapped hole vs clearance hole

The tapped hole takes the thread. The clearance hole lets the shank through so the joint is clamped by the head, not by the fastener bearing on the hole wall.

Assumptions

These are transcribed standard values, not computed ones. Inch fits come from ASME B18.2.8, metric from ISO 273, and they are the same values the thread's own reference page publishes.
Sizes the standard does not list are shown as "—", never interpolated. ASME B18.2.8 omits #12 and 9/16, so this page omits them too. A number invented to fill the gap would look exactly like a real one, which is the problem.
Metric fits are named fine / medium / coarse in ISO 273; they are keyed here as close / normal / loose so the three columns line up with the inch series.
Clearance is the hole, not the fit of the assembly. Positional tolerance, slotting for adjustment, and thermal growth are the designer's call.

Thread & tap drill charts
Tap drill calculator — the other half of the joint
Wrench & socket sizes

Data provenance. ASME B18.2.8, Clearance Holes for Bolts, Screws, and Studs (ASME). ISO 273, Clearance holes for bolts and screws (ISO). Clearance values are transcribed from ASME B18.2.8 (inch) and ISO 273 (metric) and are identical to those on each thread's reference page. Sizes absent from the standard are omitted rather than interpolated. See all data sources.

Clearance Hole Size Calculator

Tapped hole vs clearance hole

Assumptions

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